This invention relates to repair clamps for pipes which are adapted to encircle the ends of two pipes which are to be joined together or to encircle a pipe which has been damaged and thereby prevent leakage between the ends of the pipes or from the damaged portion of the pipe. Essentially such clamps are comprised of two or more opposed lugs and a flexible, usually metallic, band the ends of which are secured respectively into each of the lugs. As bolts connecting the lugs are tightened, the lugs are brought together to tighten the band around the damaged area of the pipe or around the ends of the pipe to be joined. A gasket of a suitable sealing material, such as an elastomer, is compressed between the flexible metallic band and the pipe to insure leak-type engagement between the clamp and the of the pipe or the ends of the pipe to be joined.
This invention is concerned with the means for securing the ends of the bands to the opposed lugs. One of the problems that must be overcome in designing a suitable pipe repair clamp is the tendency of the ends of the flexible band where they are secured to the lugs to pull loose from the lugs as the bolts connecting the lugs are tightened to apply tension to the band. The prior art is replete with many different proposed solutions to this problem, typical of which are shown in the following U.S. patents: Stauffer U.S. Pat. No. 2,278,714; Schustack U.S. Pat. No. 2,713,352; Schustack U.S. Pat. No. 2,826,799; Dahl U.S. Pat. No. 2,835,954; Hoke U.S. Pat. No. 2,897,568; Smith U.S. Pat. No. 2,998,629; Graham et al U.S. Pat. No. 3,089,212; Graham et al U.S. Pat. No. 3,175,267; Barr U.S. Pat. No. 3,189,970; Faint U.S. Pat. No. 3,204,665; Smith U.S. Pat. No. 3,254,387; Smith U.S. Pat. No. 3,584,353;
Many of the solutions proposed by the prior art while providing a strong band-to-lug connection, are complicated and therefore difficult and expensive to produce and assemble; others simply do not provide the requisite strength and still others require assembly operations which may weaken the lug during production of the clamp. For example, it is conventional practice to form the lugs with jaws which initially diverge from each other. During assembly of the clamp, the ends of the bands are inserted between the diverging jaws and the jaws are then coined shut against the end of the band. Protrustions may be formed on one jaw which are received into recesses formed on the other jaw to provide a strong connection between the lug and the band. Examples of such practice are shown in the patents to Graham et al. U.S. Pat. No. 3,089,212, Graham et al. U.S. Pat. No. 3,175,267, and Smith U.S. Pat. Nos. 3,254,387, 3,584,353. While the arrangement shown in these last mentioned patents may provide a strong connection between the band ends and the lug, frequently the base of the lug is weakened by the coining operation and often cracks will appear along the line of the base of the lug which defines the point about which the lower jaw is bent, thus weakening the lug.
The patent to Hoke, U.S. Pat. No. 2,897,568 shows the ends of a band which are partially wrapped around a wire and fingers on the upper portion of the bases which are coined or bent around the end of the band and the wires to secure the ends of the band onto the bases of the lugs. These fingers are, of course, subject to the same problems of reduced strength as the prior art arrangements disclosed in the patents immediately above discussed, only more so since a number of spaced fingers are employed rather than a continuous axially extending jaw. Throughout this specification and the appended claims, the terms "axial" or "axially" refers to a direction parallel to the axis of the pipe on which the clamp is mounted, and the terms "radial" or "radially" refers to a direction which is radial of the axis of the pipe on which the clamp is mounted.
Applicants have found that a suitably strong connection between the ends of the bands and the lugs may be achieved by providing an axially extending recess in the base of the lug with a slot of a radial dimension to accommodate the thickness of the band extending from the inner edge of the base to the recess, the recess having a radial dimension greater than the radial dimension of the slot. The end of the band is tightly folded back on itself one or more times, or otherwise enlarged as by welding additional metal thereto to provide an enlarged portion adapted to be received into the recess. The enlarged portion of the band end and the adjacent portion of the band may then be axially inserted into the recess and the slot respectively from either end of the lug, no coining of the jaws formed by the slot and recess being necessary. The above-mentioned patent to Barr, U.S. Pat. No. 3,189,970, in FIG. 11 shows an axially extending recess in the base of a lug and a slot which communicates with the recess. The ends of the band are folded back and are received in the recess. However, successive layers of the folded back end portions are spaced from each other and therefore the end portions do not present an essentially continuous or solid cross section. Under relatively low tensile stress in the band, as the nuts are tightened the band end portions of Barr could be unrolled and pulled through the slot. In applicants' arrangement, the enlarged band ends present an essentially solid cross section whether folded back or otherwise enlarged. Moreover, when the end of the band is tightly folded back to form an enlarged portion having a substantially solid cross section, the band material becomes cold worked in the area of the fold which increases the strength of the material or spot welding the folds to further increase the strength of retention. For these reasons it would be extremely difficult to apply sufficient tensile stress to the band to "unroll" the tight fold of applicants' band ends.
Furthermore, in Barr's arrangement, the radial dimension of the recess extends from the top surface of the slot radially inwardly toward the axis of the pipe so that the enlarged portion of the recess extends from the slot inwardly toward the axis of the pipe. Applicants have discovered that by forming the recess so that its radial dimension extends radially outward from the slot, use of the lug base material in both the upper and lower jaws is optimized and that the pull-out forces on the band must exceed the energy expanded to forming the folds in order to break applicants' band-to-lug connection; thus a significant increase in the strength of the band-to-lug connection is achieved over that provided by a recess which extends radially inward from the slot.